Protein posttranslational modifications are important for regulating protein function and are involved in numerous biological processes. Protein acetylation, controlled by acetyltransferases and deacetylases, are known to play important roles in regulation of transcription and metabolism. The acetyl donor, acetyl-CoA, is a metabolic intermediate in cells. Recently, our laboratory discovered several novel acyl lysine modifications that are structurally very different from acetyl. We have shown that these new acyl lysine modifications occur in mammalian cells and there are dedicated enzymes (sirtuins) that can remove them efficiently. These new acyl lysine modifications, like acetylation, also come from common metabolic intermediates, suggesting that these modifications may be a mechanism of sensing metabolism to regulate protein function. Studying these new modifications will allow us to better understand the chemistry of biological systems. The study has the potential to provide answers to a number of puzzles in the protein acetylation field, such as the lack of enzymatic activity for about half of the protein deacetylases. Because these acyl lysine modifications have not been studied before, no tools are available to investigate them. The existence of multiple acyl lysine modifications also adds a layer of technical complexity to the study of these modifications. The goal of this proposal is to develop new and better methods to detect and quantify these modifications and then use these methods to investigate the occurrence, regulation, and function of these modifications.